[llvm] Fix emulated TLS alignment for large variables (PR #171037)

[Eli Friedman via llvm-commits]

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efriedma-quic wrote:

DataLayout::getPreferredAlign has some weird code that increases the alignment of variables with explicitly specified alignment; see the FIXME in the implementation.  It's likely to go away in the near future, so I'd prefer to avoid extending that behavior to additional contexts in the meantime.

Maybe just use `Align GVAlignment = GV->getPointerAlignment(DL)`.

https://github.com/llvm/llvm-project/pull/171037